netdev - [PATCH net-next] net: dsa: Fix use after free in dsa_switch

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Message-Id: <20191103031326.26873-1-f.fainelli@gmail.com>
Date:   Sat,  2 Nov 2019 20:13:26 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     netdev@...r.kernel.org
Cc:     rmk+kernel@...linux.org.uk, hkallweit1@...il.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH net-next] net: dsa: Fix use after free in dsa_switch_remove()

The order in which the ports are deleted from the list and freed and the
call to dsa_tree_remove_switch() is done is reversed, which leads to an
use after free condition. Reverse the two: first tear down the ports and
switch from the fabric, then free the ports associated with that switch
fabric.

Fixes: 05f294a85235 ("net: dsa: allocate ports on touch")
Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
 net/dsa/dsa2.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index ff2fa3950c62..9ef2caa13f27 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -874,12 +874,13 @@ static void dsa_switch_remove(struct dsa_switch *ds)
 	struct dsa_switch_tree *dst = ds->dst;
 	struct dsa_port *dp, *next;
 
+	dsa_tree_teardown(dst);
+
 	list_for_each_entry_safe(dp, next, &dst->ports, list) {
 		list_del(&dp->list);
 		kfree(dp);
 	}
 
-	dsa_tree_teardown(dst);
 	dsa_tree_put(dst);
 }
 
-- 
2.17.1